This invention relates to a medium clamp mechanism, and more particularly to a medium clamp mechanism for fixing to a drive device a medium onto and from which information can be recorded and read out by rotating it on such a drive device loaded therewith.
As such media, there are floppy disks, direct access memory devices, video disks, and so on. However, the following description will be given generally in connection with floppy disks. In detailed construction, a floppy disk includes a disk which is called a medium and a jacket which contains the disk therein. It is to be noted, however, that the terms "medium" and "floppy disk" designate the same item all through the present specification.
A typical one of conventional medium clamp mechanisms in drive units for fixing and rotating such a medium loaded thereon will be first described with reference to FIGS. 1 and 2. The illustrated medium clamp mechanism includes a spindle 3 which extends through a frame 1 via a bearing 2. A pulley 4 is mounted at one end of the spindle 3 for integral rotation therewith. A medium 5 is received on the top of the pulley 4. A hub frame 6 is disposed above the medium 5, and a hub shaft 7 extends through the hub frame 6. A hub 8 is disposed around an end of the hub shaft 7 opposing to the pulley 4. A collet 10 is located around a bearing 9 above the hub 8 and is resiliently connected to the hub 8 by means of a spring 11. Also, the bearing 9 is resiliently connected to the inner wall of the hub frame 6 by means of a washer 12 and a spring 13. An E snap ring 14 is disposed at the other end of the hub shaft 7 which extends upwardly through the hub frame 6. Thus, the hub frame 6, the hub 8 and the collet 10 are resiliently interconnected in concentrical relationship around the hub shaft 7. In a medium clamp mechanism which has such a structure described just above, an inner bore of the pulley 4 is designed to have a diameter approximated to the diameter of a center clamp hole of the media 5 so that a clamping force can cause the collet 10 to slightly expand the hub 8 thereby to allow clamping and centering of the medium, as can be seen from an enlarged view of FIG. 2. Upon release, the collet spring 11 will push up the collet 10 to render the hub 8 free, thereby releasing clamping of the medium 5.
However, a conventional medium clamp mechanism which has such a construction as described just above has a defect that it cannot be well accommodated to variations in the diameter of center holes of media, resulting in unsatisfactory accuracy of centering of media, and besides, inward deformation of a hub upon clamping will further deteriorate such centering. Moreover, according to such a structure as described above, it has another defect that desired performances could not be attained without individual parts finished in high accuracy.